1. Field of the Invention
The present invention relates to a computer graphics, and more particularly, to a system and a method for measuring reflectance of an object for modeling a realistic image of an object.
2. Description of the Related Art
A function representing characteristics of the surface of an object by using an incident angle and a reflection angle of light emitted from a light source is referred to as a bi-directional reflectance distribution function (BRDF) at the time of modeling a realistic image of the object. The BRDF is defined as a ratio of incident energy flux and radiance of light reflected on the surface of the object.
Information on reflectance of the object is generally represented by the BRDF. An image of the object can be simulated by calculating reflection energy of the object to the light source by using the reflectance of the object. That is, it is possible to simulate the image of the object generally existing on a circumference, which can be seen in a photograph or seen by a human at a place where the light source is provided.
In general, in order to measure the BRDF of the object, the light sources are disposed at all locations where the light sources can influence the object and the reflection energy of the object is measured at each of the locations. The BRDF of the object can be acquired by expressing a result calculated by measuring all reflection energy to the light sources incident in all the directions by a 4-dimensional function expressed, for example, in the following equation in a polar coordinate system (or spherical coordinate system).
                                          f            r                    ⁡                      (                                          θ                i                            ,                              Φ                i                            ,                              θ                r                            ,                              Φ                r                                      )                          =                                            ⅆ                                                L                  r                                ⁡                                  (                                                            θ                      r                                        ,                                          Φ                      r                                                        )                                                                    ⅆ                                                E                  i                                ⁡                                  (                                                            θ                      i                                        ,                                          Φ                      i                                                        )                                                              =                                    ⅆ                                                L                  r                                ⁡                                  (                                                            θ                      r                                        ,                                          Φ                      r                                                        )                                                                                                      L                  i                                ⁡                                  (                                                            θ                      i                                        ,                                          Φ                      i                                                        )                                            ⁢              cos              ⁢                                                          ⁢                              θ                i                            ⁢                              ⅆ                                  ω                  r                                                                                        [                  Equation          ⁢                                          ⁢          1                ]            
The general BRDF measurement system is constituted by a 4 degree-of-freedom system consisting of two incident angles and two reflection angles. However, this system has a disadvantage of incurring a lot of expenses due to an excessive measurement time of several hours or several tens of hours and massive measurement data in order to acquire information on all direction angles.